This invention relates to a brake system control method and apparatus.
Many automobiles include anti-lock brake systems as standard or optional features. Some automobiles include traction control systems for preventing wheel slip during positive acceleration of the vehicle. Anti-lock brake systems and many traction control systems utilize wheel speed sensors that provide individual wheel speed information to the brake controller allowing the controller to perform its anti-lock and/or traction control functions. Vehicles have also been provided with a telltale in the instrumentation panel that illuminates when the anti-lock brake system and/or traction control system is activated to indicate to the driver that the vehicle may be on a road surface with low traction or a low coefficient of friction.
In operation, typical anti-lock brake systems monitor the wheel speeds of the vehicle wheels and determine a normalization factor for each wheel. This normalization factor is designed to offset differences in wheel rolling radii due to uneven weight distribution of the vehicle on the wheels, uneven tire fill pressures, etc. Typically, the normalization factors are continuously updated, except when the vehicle is in anti-lock brake control mode or traction control mode.
It is an object of this invention to provide a brake control system according to claim 1.
Advantageously, this invention provides a brake system control for scrutinizing wheel speed signals from wheel speed sensors and determining normalized wheel speed signals with increased accuracy. Advantageously, this invention uses the measured wheel speed signals to determine normalization factors for the vehicle wheels and uses the normalization factors to determine the normalized wheel speeds. Advantageously, this invention inhibits updating the normalization factors in a variety of wheel conditions that would provide contaminated wheel speed information, otherwise impairing the accuracy of the normalization factors and, thus, the normalized wheel speed signals.
Advantageously, the criteria used to determine whether the normalization factors are to be updated are stricter than previously known and the result is that the normalized wheel speeds determined according to this invention have improved accuracy.
Advantageously, this invention provides a brake system control that monitors the vehicle wheel speed information as provided by the vehicle wheel speed sensors and analyzes that information against a variety of criteria to determine whether normalization factors should be updated. If any of the tests indicate that the wheel speed information is not sufficiently free from contamination due to road conditions, the wheel normalization factors are not updated. Additionally, in a preferred example, each time that the system detects that the wheel speed information may be contaminated due to road conditions, a timer is updated and, when the timer reaches a predetermined threshold, a telltale, chime, or other signal for the driver is activated.